Conventionally, foam dispensing pump containers based on the method of storing a high-pressure gas, e.g., a carbon dioxide gas and a Freon gas, in a container together with a foamable liquid for creating foam upon dispensing are in wide and practical use. With the growing public consciousness for the global environment in these years, however, there have been apparent moves for totally banning use of such kinds of high-pressure gases in an attempt to protect the global atmosphere. Accordingly, demands have arisen for a foam dispensing pump container not using the high-pressure gas.
Japanese Utility Model Registration No. 1529456 (Japanese Utility Model Publication No. 58-23415) discloses a typical example of a foam dispensing pump container not using a high-pressure gas. The proposed arrangement according to this disclosure may be briefed as follows. That is, this foam dispensing pump container comprises a double cylinder which is provided at an opening portion of a container containing a liquid and which is constituted by air and liquid cylinders that are concentrically provided, a dip tube for allowing a bottom portion of the liquid cylinder and a bottom portion of the container to communicate with each other, a piston assembly constituted by air and liquid pistons integrally provided and movable up and down in the air and liquid cylinders, respectively, a nozzle member provided at an upper end of the piston assembly and having a foam dispensing hole portion, an air flow path for allowing the hole portion and the air cylinder to communicate with each other, a liquid flow path for allowing the liquid cylinder and the hole portion to communicate with each other, a first check valve disposed midway along the liquid flow path, a second check valve disposed in the liquid cylinder, a compression spring for urging the piston assembly to a top dead point with respect to the double cylinder, a lid member for fixing the double cylinder to the container and defining the air cylinder to guide insertion of the piston assembly therethrough, and an interposed permeable object or a porous member, e.g., a sponge, having a function of introducing outer air and generating and discharging foam at a juncture of the air flow path and the liquid flow path in the hole portion.
With the above arrangement, when the piston assembly moves up and down, the liquid supplied from the liquid cylinder and air supplied from the air cylinder are mixed in the interposed permeable object to generate foam and dispense it through the hole portion of the nozzle member.
However, the aforementioned interposed permeable object of this proposal has the first problem in that, since it has has two functions, i.e., a function of introducing the outer air into the air cylinder and a function of generating and discharging the foam, the fluid resistance upon introduction of the outer air essentially becomes large enough to disturb smooth reciprocal movement of the piston assembly. The interposed permeable object also has a second problem. That is, the liquid component of the foam remaining in the interposed permeable object gets dry and solidified in it thereby, causing clogging.
Japanese Utility Model Registration No. 1467526 (Japanese Utility Model Publication No. 57-20285), which is filed by the same applicant as Japanese Utility Model Registration No. 1529456 described above, proposes another foam dispensing pump container not using a high-pressure gas. According to this second proposal, the double cylinder in the arrangement of above Japanese Utility Model Registration No. 1529456 is provided with the liquid cylinder which stands at the central portion of the bottom portion of the air cylinder, an outer air inlet hole having an operational valve is formed in the air cylinder to allow the liquid in the container to communicate with outer air outside the container in order to prevent the interior of the container from being set at a negative pressure, and the skirt portion of the air piston which slides on the inner surface of the air cylinder is formed thin.
However, the second proposal does not clearly describe a means for introducing outer air into the air cylinder and if the same arrangement as the first proposal is in use, it still has the same problems. Also, if the skirt portion of the air piston which slides on the inner surface of the air cylinder is to be formed thin so that the skirt portion is deformed inward when the interior of the air cylinder is set at the negative pressure, thereby introducing outer air into the air cylinder, high precise slidable contact between the air cylinder and the air piston must be maintained.
Even if such precise sliding contact is obtainable, sufficient air supply cannot be attained when the piston is slightly inclined while it is moved downward, and as a result, the quantity of air supplied to the interposed permeable object essentially varies and a constant mixing ratio of the air and liquid cannot be maintained.